The present invention relates generally to time gating devices and more specifically to those devices for supplying blanking pulses to receivers for the purpose of desensitizing them during the transmit time of certain friendly emitters. The present invention also relates to blanking systems utilizing monostable multivibrators or one-shots and to the recovery time aspects thereof.
A Navy blanking system, the AN/SLA-10A, is a time gating device which supplies blanking pulses to receivers for the purpose of desensitizing them during the transmit time of certain friendly emitters. In order to function properly, the AN/SLA-10A system must receive a trigger pulse that precedes the actual transmission by some known amount of time. Knowing this time, the width of the transmitted pulse and the measure of pulse stretching due to sea reflections, the required delay and width of the blanking pulse for that particular emitter can be determined. Each potentially interfering emitter feeds its pretrigger pulse into a separate channel of the AN/SLA-10A. The delay function is implemented by generating a pulse in a monostable multivibrator or one-shot and using the trailing edge of that pulse as a delay trigger for follow-on circuits. The required delay can, therefore, be set by adjusting the pulse width of the delay one-shot.
Relatively recent requirements have evolved for equipment to generate very high pulse-repetition-frequency (PRF) blanking pulses to minimize interference from certain high-PRF radars and some high data rate digital communication systems. Due to the relatively long recovery time of the delay one-shots of the AN/SLA-10A blanking system, it is not capable of handling these high-PRF signals.
At the trailing edge of its output pulse, a conventional one-shot will not have completely returned to its stable state. It requires additional time in which to allow transients in its timing circuit to decay to zero. This trailing edge transient period is referred to as recovery time. The fact that the one-shot must not be triggered during recovery time imposes a fundamental limitation upon the maximum PRF and duty cycle it can achieve. The recovery times associated with prior art one-shots, in particular the one-shots in the AN/SLA-10A have, from an operational standpoint, limited present equipment to a maximum blanking frequency far below that necessary to satisfy the previously mentioned requirements of high-PRF radars and high data rate digital communication systems.